I had forgotten that in the town of Chartres, close to the cathedral, there is a dolls' hospital. In her new novel, ex-psychoanalyst Salley Vickers vividly evokes this strange conjunction – the sublime grandeur of one of the most beautiful religious buildings in the world and the poignant smallness, the peculiar shabbiness, of once loved, now broken, toys.

The novel centres on mysterious and beautiful Agnès Morel, a foundling raised by nuns, who works as the cathedral's cleaner in her 40s. She is a recessive, taciturn character, through whom a wide range of people living in Chartres, or visiting it, reveal themselves. Vickers assembles her story in fragments, like a stained-glass window. As they relate to Agnès – often talking to her while she works – priests, nuns, pilgrims, tourists, artists and shopkeepers make cameo appearances, building towards a broad picture of the town.

The cathedral dominates the beginning of the novel, which opens in the manner of a guidebook: "Five successive cathedrals have stood on this site; all were burned to rubble save the present cathedral, which grew, phoenix-like from the embers of the last devastating fire. On 10 June 1194, flames sped through Chartres, destroying many of the domestic dwellings, crowded cheek by jowl in the narrow medieval streets, and all the former cathedral save the western front with its twin towers and the much more ancient crypt."

The character of Agnès, preoccupied with the mundane task of cleaning, allows Vickers to move out of the cathedral's imposing shadow, to describe small parts of it in minute detail. The strange maze, or labyrinth, set into the floor of the nave just inside the west doors, fascinates Agnès: "A cross was adumbrated by the bands of black marble that marked the turns in the path. It was clever, she reflected, the cross, being composed not of the stones that made the path but of those that marked its absence."

Absence is at the heart of Agnès's life. Found half-frozen in a basket by a farmer, who did not think himself capable of raising a female baby, she lived in a convent until becoming pregnant as a teenager (a feat, in the circumstances). When the baby was forcibly taken from her, she went mad.

Vickers reveals Agnès's story in layers, circling between the past and present, cumulatively deepening the narrative. The technique has much in common with psychoanalytical methods, not least in the role that silence plays.

Agnès is often offered cleaning jobs outside the cathedral. She finds it difficult to refuse new work or to demand proper payment. Her vulnerability is a foil for other people's unpleasantness.

Most objectionable of all her employers is spiteful Madame Beck, an obsessive collector of china dolls. She unjustly accuses Agnès of breaking or stealing one of her dolls and insists she works free of charge to recover the cost.

The visit to the dolls' hospital is unforgettably creepy: "Albert the Doll Doctor hated his patients to leave his care. The little girls who sent their toys for repair had to beg and wheedle them out of him with sworn assurances of treating their charges better in the future."

Never ponderous, The Cleaner of Chartres touches lightly but knowingly on the seedy side of human nature. Up against Agnès's fairytale goodness, the other characters huddle like the ramshackle domestic buildings that once filled the medieval streets surrounding the cathedral on its hilltop.

In interviews, Vickers has said that she stopped practising as a psychoanalyst two years after she published her first novel, Miss Garnet's Angel (2000): "The two things just weren't compatible because the work comes from the same place." Her new novel suggests that the relation between her two professions remains as dynamic as ever.